Experimental Research On Dynamic Mechanical Properties And Characteristics Of Wood Composite

With the developments and researches of bamboo-wood composite materials, theutilization of bamboo resources and products have been improved and widen, thus helpalleviate the shortage of wood supply resulted from natural forest protective project. Bamboomaterials are strong, tenacious and wear-resisting but have longer periods, smaller outturnpercentage, greater processing difficulty and lower efficiency. Meanwhile, fast-growing trees(poplar, fir, etc.) are easy to process and more efficient but have less mechanical strength andlower surface hardness. Bamboo-wood composite materials can give effective play of theadvantages of these two types of wood since bamboo-wood composite materials are producedin a scientific reasonable combination of them through adhesion. This research starts from theconcept of material design and provides an active design method of bamboo-wood compositematerials. In the beginning, there is an analysis of the performance test of component materials,and then make a model for the prediction of strength considering production technology. Afterthat, experimental researches of dynamic characteristics of bamboo-wood composite materialsare made using modal analysis technique and test researches of absorption ability of componentmaterials and bamboo-wood composite materials are made through PULSE.When designing bamboo-wood composite materials, the structural design and design ofcomposite materials are made simultaneously and different composite materials with differentcharacteristics are produced when ratio governing changes. Experiments in which tensile andflexural properties of component materials—poplar and bamboo are tested the samples aretreated normally, under pressure or adhesive-soaked are made in the method of orthogonal tablein order to study the influences of longitudinal and transverse elastic and strength (tensile andcompressive) properties and orthogonality on the mechanical properties of component materials.The research shows that in the normal condition, longitudinal tensile strength and elasticmodulus of poplar veneers increase when veneers are thicker but they are non-linearly related.Under different pressure, there is no proportionality between longitudinal tensile strength andelastic modulus of poplar veneers. When pressure increases, elastic properties will even comedown and longitudinal tensile strength and elastic modulus keeps going up. Under the normalpressure, Longitudinal tensile strength and elastic modulus, flexural elastic properties andbending strength of poplar veneers of different thickness increase as pressure increases,showing a quadratic parabola relationship. All numbers of longitudinal tensile strength of testpoplar veneers of adhesive-soaking have greatly improved compared with poplar veneers underpressure in normal condition. Longitudinal tensile strength and elastic modulus, flexural elasticproperties and bending strength all shows a non-linearly relationship with adhesive pressure and by regression analysis, it appears to be a quadratic parabola relationship. When transversetensile strength is smaller than5MPa, transverse flexural strength falls between several MPaand a dozen or more MPa, showing transverse tensile properties and anti-flex characteristics ofpoplar veneers are quite inferior.Predictions of effective elastic modulus are made since elastic properties of componentmaterials are understood. Bamboo-wood composite material is considered as evenly orthotropicmaterial for its stepped construction. Predicting model of longitudinal effective elastic model ofbamboo-wood composite beam is analyzed using classic laminated theory and flexural strengthmodulus and elastic modulus and model of bamboo-wood composite beam is developedrespectively through principle of minimum potential energy and the equivalent beam theory.After substituting tensile and elastic modulus as well as flexural bending modulus;bendingelastic modulus in the model, it can be calculated that the measured number of flexural elasticstrength is9.93%smaller than calculated and the measured number of flexural elastic modulusis4.84%smaller than calculated.modal analysis theory and transverse flexural vibration theory are used to analyze andstudy the dynamic characteristics of bamboo-wood composite materials and two calculationmodel are based:Euler-Bernoulli beam and Timoshenko beam’s transverse bending vibrationdifferential equations are used to calculate its frequency equation and dynamic elasticequations. To provide rationale and reference for further study and utilization ofbamboo-wood composite materials, impulse excitation test is used to study their dynamiccharacteristics and modal parameters (natural frequency and damping ratio), dynamic elasticmodulus、physical parameter and non-reference models of this new composite material areanalyzed and calculated with CRAS V5.1through analysis and comparism of resonance andthree-point bending methods.Tests of absorption coefficient are made of poplar veneers and bamboo-wood compositeboard with professional PULSE acoustic test system produced by B&K company. The researchresults turn out that both show a better performance when absorbing high-pitch sounds; thepoplar veneer has an obvious better performance in absorbing high-pitch sounds than low-pitchsounds and thickness has a clear influence of medium-high-pitch sound which means thethinner the veneer is, the greater the absorption coefficient, the greater acoustic absorption bandand absorbing ability is; bamboo-wood composite materials are proved to be unfit for absorbingmaterial for the minute absorption coefficient.